Thermo-mechanical characterization of unsaturated polyester/glass fiber composites for recycling

Unsaturated-polyester/glass-fiber composites are worldwide more and more used. Actually, their thermochemical and mechanical recycling paths are quite well-known. But, due to the relatively low value of the end products, these two paths are hardly economically viable. Thus, a third way will be proposed as a thermomechanical path. In order to recycle these composites, a study of their thermo-mechanical behaviors is proposed in this work, through various static and dynamic tests at temperatures ranging from ambient to 150 °C, over their glass-transition-temperature (Tg). As expected, the results prove that unsaturated-polyester reinforced by woven glass-fibers is more resistant in static flexion and traction than composite made with mixed chopped and woven glass-fibers, at ambient temperature and up to 150 °C. Also, static and dynamic tests have shown that composite manufactured by infusion is more resistant than the hand lay-up composite forming. Indeed, dynamic 3-points-flexural-bending test indicates that these composites lose their stiffness during the temperature rise. Furthermore, the composites ageing study shows the appearance of Mullins effect and hysteresis phenomena, at 150 °C. After an accelerated ageing in distilled water at ambient temperature, the composite lost about 66% of its flexural resistance but a gain of 195% in its deformation at break is obtained. For an ageing in distilled water at temperature around its Tg, this composite lost the same ratio in its flexural resistance but got 180% in its yield deformation, compared to its virgin state. The mechanical properties lose can be interpreted by the ester function hydrolysis and the glass fibers damage.